Arthroscopy is a surgical procedure in which a camera, attached to a remote light source and video monitor, is inserted into an anatomic joint (e.g., knee, shoulder, etc.) through a small portal incision in the overlying skin and joint capsule. Through similar portal incisions, surgical instruments may be placed in the joint, their use guided by arthroscopic visualization. As arthroscopists' skills have improved, an increasing number of operative procedures, once performed by “open” surgical technique, now can be accomplished arthroscopically. Such procedures include, for example, partial meniscectomies and ligament reconstructions in the knee, shoulder acromioplasties and rotator cuff debridements and elbow synovectomies. As a result of widening surgical indications and the development of small diameter arthroscopes, wrist and ankle arthroscopies also have become routine.
Throughout each arthroscopy, physiologic irrigation fluid (e.g., normal saline or lactated Ringer's) is flushed continuously through the joint, distending the joint capsule and removing operative debris, thereby providing clearer intra-articular visualization. U.S. Pat. No. 4,504,493 to Marshall discloses an isomolar solution of glycerol in water for a non-conductive and optically clear irrigation solution for arthroscopy.
Alleviating pain and suffering in postoperative patients is an area of special focus in clinical medicine, especially with the growing number of out-patient operations performed each year. The most widely used agents, cyclooxygenase inhibitors (e.g., ibuprofen) and opioids (e.g., morphine, fentanyl), have significant side effects including gastrointestinal irritation/bleeding and respiratory depression. The high incidence of nausea and vomiting related to opioids is especially problematic in the postoperative period. Therapeutic agents aimed at treating postoperative pain while avoiding detrimental side effects are not easily developed because the molecular targets for these agents are distributed widely throughout the body and mediate diverse physiological actions. Despite the significant clinical need to inhibit pain and inflammation, methods for the delivery of inhibitors of pain and inflammation at effective dosages while minimizing adverse systemic side effects have not been developed. As an example, conventional (i.e., intravenous, oral, subcutaneous or intramuscular) methods of administration of opiates in therapeutic doses frequently is associated with significant adverse side effects, including severe respiratory depression, changes in mood, mental clouding, profound nausea and vomiting.
Prior studies have demonstrated the ability of endogenous agents, such as serotonin (5-hydroxytryptamine, sometimes referred to herein as “5-HT”), bradykinin and histamine, to produce pain and inflammation. Sicuteri, F., et al., Serotonin-Bradykinin Potentiation in the Pain Receptors in Man, Life Sci. 4, pp. 309-316 (1965); Rosenthal, S. R., Histamine as the Chemical Mediator for Cutaneous Pain, J. Invest. Dermat. 69, pp. 98-105 (1977); Richardson, B. P., et al., Identification of Serotonin M-Receptor Subtypes and their Specific Blockade by a New Class of Drugs, Nature 316, pp. 126-131 (1985); Whalley, E. T., et al., The Effect of Kinin Agonists and Antagonists, Naunyn-Schmiedeb Arch. Pharmacol. 36, pp. 652-57 (1987); Lang, E., et al., Chemo-Sensitivity of Fine Afferents from Rat Skin In Vitro, J. Neurophysiol. 63, pp. 887-901 (1990).
For example, 5-HT applied to a human blister base (denuded skin) has been demonstrated to cause pain that can be inhibited by 5-HT3 receptor antagonists. Richardson et al., (1985). Similarly, peripherally applied bradykinin produces pain that can be blocked by bradykinin receptor antagonists. Sicuteri et al., 1965; Whalley et al., 1987; Dray, A., et al., Bradykinin and Inflammatory Pain, Trends Neurosci. 16, pp. 99-104 (1993). Peripherally-applied histamine produces vasodilation, itching and pain that can be inhibited by histamine receptor antagonists. Rosenthal, 1977; Douglas, W. W., “Histamine and 5-Hydroxytryptamine (Serotonin) and their Antagonists”, in Goodman, L. S., et al., ed., The Pharmacological Basis of Therapeutics, MacMillan Publishing Company, New York, pp. 605-638 (1985); Rumore, M. M., et al., Analgesic Effects of Antihistaminics, Life Sci 36, pp. 403-416 (1985). Combinations of these three agonists (5-HT, bradykinin and histamine) applied together have been demonstrated to display a synergistic pain-causing effect, producing a long-lasting and intense pain signal. Sicuteri et al., 1965; Richardson et al., 1985; Kessler, W., et al., Excitation of Cutaneous Afferent Nerve Endings In Vitro by a Combination of Inflammatory Mediators and Conditioning Effect of Substance P, Exp. Brain Res. 91, pp. 467-476 (1992).
In the body, 5-HT is located in platelets and in central neurons, histamine is found in mast cells, and bradykinin is produced from a larger precursor molecule during tissue trauma, pH changes and temperature changes. Because 5-HT can be released in large amounts from platelets at sites of tissue injury, producing plasma levels 20-fold greater than resting levels (Ashton, J. H., et al., Serotonin as a Mediator of Cyclic Flow Variations in Stenosed Canine Coronary Arteries, Circulation 73, pp. 572-578 (1986)), it is possible that endogenous 5-HT plays a role in producing postoperative pain, hyperalgesia and inflammation. In fact, activated platelets have been shown to excite peripheral nociceptors in vitro. Ringkamp, M., et al., Activated Human Platelets in Plasma Excite Nociceptors in Rat Skin, In Vitro, Neurosci. Lett. 170, pp. 103-106 (1994). Similarly, histamine and bradykinin also are released into tissues during trauma. Kimura, E., et al., Changes in Bradykinin Level in Coronary Sinus Blood After the Experimental Occlusion of a Coronary Artery, Am Heart J. 85, pp. 635-647 (1973); Douglas, 1985; Dray et al. (1993).
In addition, prostaglandins also are known to cause pain and inflammation. Cyclooxygenase inhibitors, e.g., ibuprofen, are commonly used in non-surgical and post-operative settings to block the production of prostaglandins, thereby reducing prostaglandin-mediated pain and inflammation. Flower, R. J., et al., Analgesic-Antipyretics and Anti-Inflammatory Agents; Drugs Employed in the Treatment of Gout, in Goodman, L. S., et al., ed., The Pharmacological Basis of Therapeutics, MacMillan Publishing Company, New York, pp. 674-715 (1985). Cyclooxygenase inhibitors are associated with some adverse systemic side effects when applied conventionally. For example, indomethacin or ketorolac have well recognized gastrointestinal and renal adverse side effects.
As discussed, 5-HT, histamine, bradykinin and prostaglandins cause pain and inflammation. The various receptors through which these agents mediate their effects on peripheral tissues have been known and/or debated for the past two decades. Most studies have been performed in rats or other animal models. However, there are differences in pharmacology and receptor sequences between human and animal species. There have been no studies conclusively demonstrating the importance of 5-HT, bradykinin or histamine in producing postoperative pain in humans.
Furthermore, antagonists of these mediators currently are not used for postoperative pain treatment. A class of drugs, termed 5-HT and norepinephrine uptake antagonists, which includes amitriptyline, has been used orally with moderate success for chronic pain conditions. However, the mechanisms of chronic versus acute pain states are thought to be considerably different. In fact, two studies in the acute pain setting using amitriptyline perioperatively have shown no pain-relieving effect of amitriptyline. Levine, J. D., et al., Desipramine Enhances Opiate Postoperative Analgesia, Pain 27, pp. 45-49 (1986); Kerrick, J. M., et al., Low-Dose Amitriptyline as an Adjunct to Opioids for Postoperative Orthopedic Pain: a Placebo-Controlled Trial Period, Pain 52, pp. 325-30 (1993). In both studies the drug was given orally. The second study noted that oral amitriptyline actually produced a lower overall sense of well-being in postoperative patients, which may be due to the drug's affinity for multiple amine receptors in the brain.
Amitriptyline, in addition to blocking the uptake of 5-HT and norepinephrine, is a potent 5-HT receptor antagonist. Therefore, the lack of efficacy in reducing postoperative pain in the previously-mentioned studies would appear to conflict with the proposal of a role for endogenous 5-HT in acute pain. There are a number of reasons for the lack of acute pain relief found with amitriptyline in these two studies. (1) The first study (Levine et al., 1986) used amitriptyline preoperatively for one week up until the night prior to surgery whereas the second study (Kerrick et al., 1993) only used amitriptyline postoperatively. Therefore, no amitriptyline was present in the surgical site tissues during the actual tissue injury phase, the time at which 5-HT is purported to be released. (2) Amitriptyline is known to be extensively metabolized by the liver. With oral administration, the concentration of amitriptyline in the operative site tissues may not have been sufficiently high for a long enough time period to inhibit the activity of postoperatively released 5-HT in the second study. (3) Since multiple inflammatory mediators exist, and studies have demonstrated synergism between the inflammatory mediators, blocking only one agent (5-HT) may not sufficiently inhibit the inflammatory response to tissue injury.
There have been a few studies demonstrating the ability of extremely high concentrations (1%-3% solutions—i.e., 10-30 mg per milliliter) of histamine) (H1) receptor antagonists to act as local anesthetics for surgical procedures. This anesthetic effect is not believed to be mediated via H1 receptors but, rather, due to a non-specific interaction with neuronal membrane sodium channels (similar to the action of lidocaine). Given the side effects (e.g., sedation) associated with these high “anesthetic” concentrations of histamine receptor antagonists, local administration of histamine receptor antagonists currently is not used in the perioperative setting.